A meta-page is a web page without content that is configured to show how items of a given model should be presented when each has its own URL. In other words, many items share one meta-page, and thus share the same basic design and layout.
By way of an example, say a 'blog post' model, all blog posts, while containing different content, would be presented using the same meta-page: a page master template and one or more containers, and thus all look relatively similar.
In more orthodox language, a meta-page is a single-item 'view.' It takes the title and content of whichever item is being accessed, whilst keeping certain aspects of the page, such as URL structure and layout, constant from item to item.
Page elements on meta-pages
Placeholders and containers can be defined on a single meta-page to have the same value across all items. However they can also be given 'per-item' definitions for selected items of your choosing, so that the layout or content of the resulting pages can vary more, even using a single meta-page.
Item data on meta-pages
Data about the item being represented on a meta-page is accessed via the
$this variable, either as
$this.principal_item or by the model name itself, e.g.
$this.press_release where the model is called Press Release.